THE STRENGTH OF THE EARTH'S CRUST 157 



The problem may be tested in another way. 



If local compensation be true, an unusually high mountain is 

 underlain by unusually light matter and the intensity of gravity at 

 a station on its top is less than if the mountain was supported by 

 regional compensation and had matter of the mean regional density 

 below it. 



If the station is much below the average level of a mountainous 

 region, local compensation implies, on the contrary, denser matter 

 beneath and a higher value of gravity than would be given by 

 regional compensation. These relations result in the following 

 principle: For stations above the mean level, if local compensation 

 be nearer the truth the hypothesis of regional compensation would 

 tend to show its error by large negative anomalies. If regional 

 compensation be nearer the truth, the hypothesis of local compensa- 

 tion would tend to show its error by giving large positive anomalies. 

 For stations below the mean level the reverse would be true. But 

 for any individual station other departures from the truth of that 

 hypothesis of isostasy which gives the basis for the calculations may 

 have greater influences and give larger anomalies than the question 

 to be tested. Following this principle it is stated: 



There are 22 stations in the United States in mountainous regions and 

 below the general level and the means, with regard to sign, of the anomalies 

 by the four methods of distribution are 0.000, +0.001, +0.003, ^.nd +0.005 

 dyne, while the means without regard to signs are respectively 0.017, 0.017, 

 0.018, and 0.019 dyne. For the 18 stations in the United States in mountain- 

 ous regions and above the general level the means, with regard to sign, of the 

 anomalies by the several methods of distribution of the compensation are 

 +0.003, +0.003, 0.000, and — o.io dyne. The means, without regard to 

 sign, are respectively 0.018, 0.018, 0.017, and 0.020 dyne. 



The mean, with regard to sign, of the anomalies for the stations at each 

 of the two mountain groups, indicates that the theory of regional distribution 

 of compensation to the outer limit of zone O, 166.7 kilometers is far from the 

 truth. So far as may be judged from the other average anomalies no one 

 method seems to have any decided advantage (see pp. 98-102 of Special 

 Publication No. 10).^ 



Review and analysis of the evidence. — -The present writer does not 

 see in these computations any support for the hypothesis of local 



' Bowie, 1912, p. 22. 



